1. Field of the Invention
This invention relates to telescoping booms and more particularly to telescoping boom extensions and retraction systems.
2. Prior Art
Multi-section telescoping booms are well known to the art and include, for examle, three section booms having three nestled together boom sections one of which is stationary and two of which are extensible with the innermost boom section being extensible with respect to the intermediate boom section from a forward end of the intermediate boom section and the intermediate boom section being extensible with respect to the stationary boom section from a forward end of the stationary boom section.
Such devices have, in the past, included hydraulic or pneumatic cylinders which operate between the stationary boom section and one of the extensible boom sections. Although it is known to the art to attach one end of the cylinder to the stationary section and another end of the cylinder to the most extensible of the boom sections, since the amount of extension which can exist for an ordinary cylinder is less than twice its retracted length, such devices are not favored for three section booms.
In other embodiments, a plurality of hydraulic cylinders have been used with a first hydraulic cylinder connected between the stationary and the intermediate boom section and a second hydraulic cylinder connected between the intermediate and the most extensible boom section. Such constructions have a noticeable disadvantage in requiring two cylinders and further require complicated pressure hose connections to supply pressure to the separate cylinders.
In order to reduce the complexity of such devices, it has been known to utilize chains or cables connecting various boom sections. For the most part, such prior constructions using chains or cables generally mounted the chains or cables, at least in part, exteriorly of the boom section. This external mounting, in addition to giving a bad appearance left operating portions of the system exposed to the elements and unprotected from damage or abrasion during operation.
Additionally, where such chains or cables had been previously used, it was often necessary to provide a separate take-up reel controlling actuation and take-up of the cable. Thus two actuation systems were needed, one for the hydraulic system where that was used and a second for the cable system.
It would be an advance in the art to provide a system which did not rely upon any external chains or cables and which did not require any separate actuation systems but which eliminated the necessity of multiple pneumatic or hydraulic cylinders while allowing boom extension of an amount greater than twice the collapsed length of one cylinder.